이효철 교수

Ultrafast electron diffraction (UED) has been developed to study transient structures in complex chemical reactions initiated with femtosecond laser pulses. This direct imaging of reactions was achieved using our third-generation apparatus equipped with an electron pulse (1.07 +/- 0.27 picoseconds) source, a charge-coupled device camera, and a mass spectrometer. Two prototypical gas-phase reactions were studied: the nonconcerted elimination reaction of a haloethane, wherein the structure of the

Determining 3D intermediate structures during the biological action of proteins in real time under ambient conditions is essential for understanding how proteins function. Here we use time-resolved Laue crystallography to extract short-lived intermediate structures and thereby unveil signal transduction in the blue light photoreceptor photoactive yellow protein (PYP) from Halorhodospira halophila. By analyzing a comprehensive set of Laue data during the PYP photocycle (forty-seven time points fr

We report direct structural evidence of the bridged radical (CH2ICH2.) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereo-chemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C2H4I2) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a sync

The controllable assembly behavior of diphenylalanine molecules to form nanowires (NWs) and nanotubes (NTs) and their structural details are presented (see figure). The nanoscale morphologies are closely related to molecular arrangements of diphenylalanine as revealed by Rietveld refinement of powder X-ray diffraction patterns and electron-density distributions in NTs and NWs via the maximum entropy method analysis. Detailed facts of importance to specialist readers are published as ”Supporting

Most chemical reactions occur in solution, and complex interactions between solute and solvent influence the rich chemistry of these processes. To track time-dependent processes in such reactions, researchers often use time-resolved spectroscopy. In these experiments, an optical pulse (pump) initiates a reaction, and another time-delayed optical pulse (probe) monitors the progress of the reaction. However, because of the wavelength range of the probe light used in these experiments, from infrare

The temporal diffraction-difference approach of the ultrafast electron diffraction (UED) technique was used to determine the molecular structure of the transient [Fe(CO)₄ ] formed during the elimination of CO ligands from [Fe(CO)₅ ]. The results clearly show that the major product, up to 200 ps, is the transient [Fe(CO)₄ ] which is formed in the ¹ A₁ state, rather than the ground ³ B₂ state.

Recent years have witnessed the birth of picosecond pump-probe X-ray diffraction and scattering techniques, thanks to the technological developments in the third generation synchrotron beamlines and advances in theory and data analysis by combining quantum calculations, molecular dynamics simulations and global fitting analysis. Our laboratories have employed this technique to study structural dynamics and spatiotemporal kinetics of many molecular systems in solution including diatomic molecules

We give a full account of our earlier report on the structural dynamics in the elimination reaction of C2F4I2, as studied with the newly constructed third-generation apparatus for ultrafast electron diffraction (UED3) at Caltech (Ihee, H.; Lobastov, V. A.; Gomez, U., Goodson B. M.; Srinivasan, R.; Ruan, C.-Y.; Zewail, A. H. Science 2000, 291, 458). Improvements in experimental stability, sensitivity, resolution, and versatility provided by UED3 permitted the reaction to be probed with spatial an